In order to modify their treatment, processing and use behaviour, plastics materials are for the most part provided with auxiliary substances as well as with fillers and reinforcing materials. The latter improve properties such as stiffness, strength, heat resistance, dimensional stability and reduce the thermal expansion of products based on plastics materials.
Of particular importance for plastics compositions are fillers and reinforcing materials of minerals or glass, in particular borosilicate glass or silicate glass, which is used in a very wide variety of forms, for example in the form of glass fibres, glass flocks or also in the form of expanded or foam glass. Fillers and reinforcing materials have a considerable influence on the heat deflection temperature of plastics materials. For example, when fibrous fillers having a correspondingly high length-to-diameter ratio are used, very good heat deflection temperatures are achieved. However, the anisotropic geometry of a fibre leads to the fibres being aligned in the direction of flow during processing and, associated therewith, to anisotropic shrinkage during processing, which consequently results in undesirable warpage in the products. The “wicking” associated with the fibres also leads to a deterioration of the self-extinguishing properties of these products, as are important, for example, in the glow wire test according to IEC 60695-2-12 (GWFI). In order to be able to ensure adequate flame resistance of plastics-based products even when using fibrous fillers, such as, for example, glass fibres, it is generally necessary to use halogen- or phosphorus-based flame retardants. Halogen-based flame retardants are the subject of public debate because of their accumulation in the environment. Phosphorus-based flame retardants are willingly avoided because their production is energy-intensive. In addition, there is the risk with phosphorus-containing flame retardants of corrosive deposits on electrical contacts if the product in question is an electrical component or electronic component.
Although isotropic shrinkage is obtained in products when non-fibrous fillers, in particular talc, clay minerals, mica, expanded or foam glass, are used, the moulding compositions to be used therefor and the products to be produced therefrom then frequently have unsatisfactory heat deflection temperatures (<135° C.) or inadequate self-extinguishing properties in the GWFI test at thinner wall thicknesses (<1 mm).
EP 2 468 810 A1 describes in Example 3 a polyamide-based composition which, as well as comprising melamine cyanurate, comprises ground glass and also ground chopped glass fibres. Disadvantages of this composition are its poor heat deflection temperature and, associated therewith, a considerably limited usability in electrical components, such as, for example, circuit breakers. In addition, the types of ground glass used therein to produce the glass have to undergo a very energy-intensive working step.
CN 103 013 104 A describes flame-retarded nylon-6-based compositions based on halogen-free flame retardants comprising melamine cyanurate and talc as inorganic filler.
DE 20 2014 008 6907 U1 describes a polyamide-based composition which, as well as comprising melamine cyanurate, comprises quartz powder and also chopped long glass fibres. A disadvantage of this composition is that the quartz used therein, owing to its high hardness [Mohs hardness 7 according to https://de.wikipedia.org/wiki/Quarz], results not only in increased abrasion in technical plants but also in damage to the glass fibres. Damage to the glass fibres in particular can lead to a deterioration of the mechanical properties and the heat deflection temperature of products to be produced therefrom.
A good heat deflection temperature and good mechanical properties with, at the same time, isotropic shrinkage behaviour and good self-extinguishing properties in the GWFI test are, however, an important requirement for the use of polyamide-based compositions in electronic components of complex construction, in particular in RCDs and in miniature circuit breakers (RCD=residual current device).
According to “http://de.wikipedia.org/wiki/Leitungsschutzschalter”, a miniature circuit breaker, MCB for short, also known colloquially as a safety cutout or cutout for short, is an overcurrent protective device in an electrical installation and is used in low-voltage systems. RCD refers to residual current devices (see http://de.wikipedia.org/wiki/Fehlerstromschalter).
Accordingly, the object of the present invention was to provide polymer compositions, such as polyamide compositions, which are suitable for the production of products for the electrical industry, wherein those products are distinguished by a high heat deflection temperature with, at the same time, low isotropic shrinkage behaviour, by good self-extinguishing properties in the glow wire test according to IEC60695-2-12 even at thin wall thicknesses of about 0.8 mm, and can be obtained, as compared with the prior art, using raw materials that have an alveolar, crystalline silicon dioxide content of less than 1%, have a Mohs hardness of less than 7 and are obtainable, as compared with ground glass, without an energy-intensive melting process.
According to “http://de.wikipedia.org/wiki/W%C3% A4rmeformbest%C3%A4ndigkeit”, the heat deflection temperature is a measure of the temperature resistance of plastics materials. Because of their viscoelastic material behaviour, there is no strictly defined upper use temperature for plastics materials; instead, an equivalent parameter under a defined load is used. Two standardized methods are available for that purpose, the heat deflection temperature (HDT) method and the Vicat softening temperature (VST) method.
The method for determining the heat deflection temperature described in DIN EN ISO 75-1,-2,-3 (precursor. DIN 53461) uses standard test specimens of rectangular cross-section which are subjected, preferably in the edgewise direction, to three-point bending under constant load. Depending on the height of the test specimen, in order to achieve a so-called outer fibre stress σI of 1.80 (method A), 0.45 (method B) or 8.00 N/mm2 (method C), a force F=2σIbh2/3 L, wherein b represents with width of the specimen, h represents the height of the specimen and L represents the support distance, is applied by means of weights or/and springs. The loaded specimens are then heated at a constant heating rate of 120 K/h (or 50 K/h). If the deflection of the specimen thereby reaches an outer fibre strain of 0.2%, the associated temperature is the heat deflection temperature HDT (or heat distortion temperature).
The Vicat softening temperature (VST) according to DIN EN ISO 306 (precursor: DIN 53460) is measured using a needle (having a circular cross-section of 1 mm2). The needle is loaded with a test force of 10 N (test force A) or 50 N (test force B). The test specimen having a permissible thickness of from 3 to 6.4 mm is exposed to a defined heating rate of 50 or 120 K/h. The VST is reached when the penetrator reaches a depth of penetration of 1 mm. According to the standard, the test is to be applied only in the case of thermoplastics and gives information about the practical long-term use limit, which is approximately 15 K below the Vicat temperature. Four parameter combinations are obtained by varying the boundary conditions:                VST/A50        VST/A120        VST/B50 (preferred method for comparative tests (ISO 10350-1))        VST/B120.        
According to “http://de.wikipedia.org/wiki/Schwindung#Schwindung_bei_Gie.C3.9Fharzen”, shrinkage is the change in volume of a material or workpiece without material being removed or pressure being exerted. Shrinkage occurs as a result of drying, cooling or chemical or physical rearrangement mechanisms in the material. Low shrinkage in the case of casting resins based on thermoplastics is a quality criterion, since built-in components may otherwise be exposed to compressive stress and gaps may form with respect to other parts to be wetted if there is inadequate adhesion. In the case of injection moulded products in electrical engineering/electronics, shrinkage can lead to the penetration of moisture and to reduced dielectric strength. Isotropic shrinkage is understood by the person skilled in the art as being shrinkage that is equal in an spatial directions. The shrinkage behaviour is tested in accordance with DIN EN ISO 294-4, also within the scope of the present invention.
The energy-intensive production of glass from a mixture comprising silicon oxide (SiO2), sodium oxide (Na2O) and calcium oxide as well as optionally further additives is explained in http://de.wikipedia.org/wiki/Glas. The mixture must thereby be converted into a homogeneous glass melt, for example in continuously operating ovens at temperatures of approximately 1400° C. or more. The necessary energy for melting the glass must be provided by fossil fuels or electrical energy.
Surprisingly, it has now been found that, by using nepheine syenite in the form described in greater detail below in combination with glass fibres, melamine cyanurate and optionally titanium dioxide, polyamide-based compositions yield electrical and electronics articles which have excellent properties as regards heat deflection temperature, flame resistance in the glow wire test according to IEC60695-2-12 and isotropic shrinkage behaviour, without the nepheline syenite having to be subjected to an energy-intensive melting process.